Clack valves (also known as check valves or flapper valves) are commonly used in aircraft fuel systems to control the flow of fuel between different compartments within the fuel system. A clack valve may, for example, be mounted to a rib or another wall separating two compartments of a fuel system in an aircraft wing to control the flow of fuel between the two compartments, and in particular to allow fuel to flow in one direction between the two compartments but not in the other direction.
A clack value may be designed and installed in an aircraft fuel tank such that, under positive G flight conditions, fuel can flow from a fuel tank into a collector box through the clack valve assembly, but not flow back out through it. Such an arrangement helps to ensure adequate fuel flow to the collector box under all engine feeding conditions, including gravity feed and when the quantity of fuel in the tank is low.
It is desirable to minimise the part count of clack valves in order to reduce cost, complexity, weight and assembly time and provide a rugged mechanism.